Field
The present disclosure relates to a method and circuit for driving touch sensors, wherein noise received through a finger or a conductor is measured, and a display device using the same.
Discussion of the Related Art
A user interface (UI) enables communication with a person (or user) using various electrical and electronic devices, so a user is able to easily control a device as the user wishes. Examples of the UI include a keypad, a keyboard, an on screen display (SOD), and a remote controller having an infrared communication or radio frequency (RF) communication function. A technology for the UI continues to be developed toward higher user sensitivity and manipulation convenience. The UI is evolving into a touch UI, a voice recognition UI, and a 3D UI.
A touch screen may be implemented using capacitance type touch sensors. In addition, a touch screen may be implemented using a resistive film, with an acoustic surface wave, a pressure type resistive film, and with infrared sensing. The most important factor to determine performance of such a touch screen is a signal to noise ratio (hereinafter referred to as an “SNR”). If noise introduced into a touch screen is reduced, the operation margin of a touch driving circuit can be widened and touch sensing sensitivity can be improved because an SNR value is increased.
In order to improve the SNR, a method of accurately measuring noise introduced into a touch sensor is important. Noise introduced into the touch sensor needs to be continuously measured because the noise varies in real time depending on a surrounding environment. There is known a method for improving the SNR in which the frequency of a touch sensor driving signal is changed to avoid a frequency associated with high noise. An example of such a method includes a method of changing the frequency of a touch sensor depending on the level of noise, which is disclosed in Korean Patent Application Publication No. 10-2012-0057009 (Jun. 5, 2012) of the present applicant.
A method of measuring noise in a touch sensor may include supplying a touch sensor driving signal to the touch sensor, converting output of the touch sensor when the touch sensor driving signal is supplied to the touch sensor into digital data, performing a comparison on data obtained by repeating such a method several times, and measuring noise affecting the touch sensor based on a difference between a minimum value and a maximum value according to a result of the comparison. As noise affecting a touch screen is greater, a difference between a minimum value and a maximum value is increased. However, such a noise measurement method requires a long measurement time and high current consumption because a touch sensor driving signal needs to be repeatedly applied to a touch sensor several times in order to measure noise.